1. Field of the Invention
The present invention relates to a roll control device of a vehicle such as an automobile, and more particularly, to a roll control device of a vehicle equipped with means for managing a sudden failure of means for detecting a rolling condition of the vehicle during a braking for the purpose of suppressing a rolling of the vehicle, the braking being controlled based upon the output of the rolling condition detection means.
2. Description of the Prior Art
As a roll control device of a vehicle such as an automobile, there is known a device described in Japanese Patent Laid-open Publication 6-297985 by the same applicant as the present application, wherein a parameter for judging a liability of the vehicle to roll down is calculated based upon a height of the center of gravity and a roll angle of the vehicle, so that a braking force is applied to a selected wheel or wheels for decelerating and suppressing the vehicle from rolling down when the parameter exceeds a predetermined threshold value. By such a roll control device, the vehicle is automatically suppressed from rolling so much as to approach a limit of rolling down during a turning, thereby relieving the driver from the requirement of a keen attention about a rolling condition or a control of vehicle speed during a turning.
In a roll control of a vehicle such as above, it is generally required to detect at least a lateral acceleration of the vehicle as a parameter for detecting a rolling condition of the vehicle for judging a requirement of the roll suppress control. When the lateral acceleration sensor does not operate normally, the roll control device does not operate normally. Therefore, when a failure has occurred in the lateral acceleration sensor, or more generally, in the rolling condition detection means including sensors such as the lateral acceleration sensor, the roll control device should no longer be operated. Further, if a failure of the lateral acceleration sensor or the rolling condition detection means occurred during the operation of the roll control device, the operation of the roll control device will have to be stopped as soon as possible.
In the known roll control devices, including that of the above-mentioned laid-open publication, when the roll control ends, the braking applied for the roll suppress purpose is generally rapidly canceled so that the vehicle is resumed as soon as possible to the normal control of the driver. When the braking is canceled according to a normal brake ending schedule at a normal end of the brake control that the rolling condition of the vehicle subsided below a predetermined threshold value, a cancellation of the braking at a relatively high speed will cause no shock or instability of the vehicle. However, if the braking is canceled according to the same normal brake ending schedule from a relatively large vehicle rolling condition due to an occurrence of a failure of a lateral acceleration sensor or rolling condition detection means during the operation of the roll suppress control, there would occur a substantial shock or instability of the vehicle.